(1) Field of the Invention
The present invention relates to a sheet discharge processing device which can discharge sheets on which images are formed by an image forming apparatus, with the discharged pages being sorted in order.
The present invention also relates to a sheet discharge processing device which aligns discharged sheets in a state sorted in order of page while discharging the sheets on which images are formed by an image forming apparatus, and which performs post-processing for a bundle of the aligned sheets, e.g., stapling, punching, or pasting.
(2) Description of the Prior Art
Recently, a digital copying machine as an image forming apparatus has been commercialized as a multi-function machine which operates in the printer mode, the facsimile mode, and the like as well as in the copy mode. In the general copy mode, sheets of paper are sequentially discharged facing up, i.e., with the image-bearing surfaces facing up. In the printer or facsimile mode, face-down paper discharge, i.e., paper discharge with each image-bearing surface facing down, is generally performed. More specifically, in the general copy mode, in consideration of the collation of image-bearing sheets to be discharged, an automatic document feeder or the like is used to feed originals so as to cause the machine to sequentially form images on sheets from the last page, thereby discharging image-bearing sheets in the collated or sorted state.
In contrast to this, when the machine operates as a printer or facsimile apparatus, since image data are sequentially transferred from an external device such as a wordprocessor and personal computer from the first page, image formation is performed from the first page. For this reason, in the copy mode, sheets must be discharged without changing their states. In the printer mode, sheets must be discharged onto a discharge tray after they are reversed, with the image-bearing surfaces facing down.
In order to realize this sheet discharge processing function, for example, Japanese Patent Application Laid-open Hei 5 No. 310357 discloses a device. The arrangement of this device will be briefly described below. As shown in FIG. 27, when a toner image on a photoreceptor 101 is transferred onto a sheet fed from a paper feed tray 100, the sheet passes through a fixing device 102 and is discharged out of the device. A paper discharge processing unit 103 switches the sheet discharge modes in accordance with the copy mode or the printer mode.
When the image forming apparatus is in the copy mode, the sheet is discharged, with the recording surface facing up, onto a first discharge tray 105 through a paper outlet 104 via various convey rollers of a paper discharge processing unit 103. In the printer mode, the convey path is switched to temporarily guide the sheet to a switchback convey path 106 via various convey rollers, and the convey direction is switched by a switching means 107. Thereafter, the sheet is discharged, with the image-bearing surface facing down, onto a second discharge tray 109 through a paper outlet 108.
Referring to FIG. 27, reference numeral 110 denotes an intermediate unit for double-sided image formation which is detachably or integrally mounted on a digital image forming apparatus body 111. When the intermediate unit 110 is mounted on the image forming apparatus body 111, in forming images on the upper and lower surfaces of a sheet, the sheet is conveyed into an intermediate tray 112 via the paper discharge processing unit 103 and the switchback convey path 106, and is conveyed again from the intermediate tray 112 to the transfer position on the photoreceptor 101 on which a toner image is formed.
In order to form images, a laser beam irradiation unit 113 is placed above the photoreceptor 101, and a read unit (scanner) 114 for optically reading an image on an original is placed in the uppermost portion of the apparatus. An image on an original placed on a transparent original table 115 is formed on a CCD 117 as a read element by the scanner 114 through an optical system 116. The image is photoelectrically converted and read by the CCD 117. The semiconductor laser of the laser beam irradiation unit 113 is driven on the basis of the read image data to form an image on the photoreceptor 101.
Japanese Patent Application Laid-open Hei 4 No. 247993 discloses a digital copying machine equipped with a sheet discharge processing device having a post-processing mechanism for stapling sheets on which images on originals are formed or sheets on which images received in the facsimile mode are formed. FIG. 28 shows the detailed structure of this copying machine. A toner image formed on a photoreceptor 121 is transferred onto a sheet fed from a paper feed cassette 120 by a transfer section 122. In the general copy mode, the sheet passes through a fixing device 123 and is conveyed onto a predetermined tray 125 in a sheet discharge processing device 124.
In the facsimile mode, it is checked whether a set of received images corresponds to a plurality of pages. If it corresponds to one page, the single-sided copy mode is set. If it corresponds to a plurality of pages, the double-sided copy mode is set. When the double-sided copy mode is selected, each of even-page images of the received images is formed on one surface of a sheet, the image-bearing sheet passes through the fixing device 123 and is caused to branch off by a switching pawl 126. The sheet is then guided to a reverse convey path 127. As a result, the feed direction of the sheet is reversed, and the sheet is guided onto a re-feed tray 128 with the image-bearing surface facing up. The second page, the fourth page, the sixth page, . . . are sequentially stacked on the re-feed tray 128 from the lowest portion. The sheets are sequentially fed from the re-feed tray 128 to the transfer section 122 again from the sheet of the last page (the uppermost sheet). As a result, each of odd-page images is sequentially formed on the other surface of a corresponding sheet. In this case, an (n-1)th-page image is formed on the surface opposite to the image-bearing surface of a last page n, and an (n-3)th-page image is formed on the surface opposite to the image-bearing surface of an (n-2)th page. These sheets, each having images formed on both sides, pass through the fixing device 123 and are conveyed onto a predetermined tray 125 with the odd-page surfaces facing up.
Assume that the above sheets are sequentially stacked on the tray 125 from the last page, and formation of one set of images is completed. In this case, when a staple switch 129 is operated, the sheets are stapled upon operation of a solenoid 130. A motor 131 serves to move the stapling mechanism. A bundle of sheets is stapled on the tray 125 upon operation of the solenoid 130.
In order to feed a sheet on which an image is formed in the above arrangement to the sheet discharge processing device, a switchback convey means is required to reverse the feed direction of the sheet through a switchback convey path. In order to prevent the leading and trailing ends of sheets from overlapping, the sheet convey cycle must be set on the basis of a value equal to or larger than the length of a sheet in the convey direction. As the speed of image formation on the image forming apparatus side increases, the convey speed of the switchback convey means must be set to be higher than the convey speed in the process of performing image formation. If, however, a switchback convey operation is performed at a high speed, a jam or the like may occur.
In addition, since the conventional sheet discharge processing device has paths and convey means for the above switchback convey operation, the overall size of the device increases, resulting in a disadvantage in terms of cost.
In the device disclosed in Japanese Patent Application Laid-open Hei 5 No. 310357, when sheets are to be discharged with the image-bearing surfaces facing up or down to perform post-processing such as stapling, stapling mechanisms must be mounted to be movable on the upper and lower discharge trays 105 and 109. Moving mechanisms are therefore required, and the arrangement of the device is complicated.
Furthermore, in stapling sheets, since the image-bearing surfaces are reversed, the stapling position becomes opposite, and the position of a staple is reversed. In order to make these positions uniform with respect to the image-bearing surfaces of sheets, the stapling mechanism portion becomes very complicated, resulting in a trouble or the like in a stapling operation.
In the copying machine disclosed in Japanese Patent Application Laid-open Hei 4 No. 247993, when image data received in the facsimile mode are to be read out from the memory, conveyance of sheets and image formation must be performed in consideration of the read order such that sheets are sequentially stacked on the tray 125 of the sheet discharge processing device 124 from the last page. For this reason, when a sheet convey abnormality, especially a jam, occurs in the sheet convey path, jam recovery processing becomes very complicated. Furthermore, since all facsimile image data must be temporarily stored, a large-capacity storage medium is required, and a complicated address means and the like are required to hold the stored state, resulting in an increase in cost.